A charging apparatus for a construction machine disclosed in JP2009-235717A charges a low-voltage battery with power required by solenoids for operation valves, etc., a controller for controlling them, and the like. The low-voltage battery is connected to a generator which is rotated by a drive force of an engine and power generated by the generator is charged into the low-voltage battery.
When the low-voltage battery is fully charged, the generator is idled with no load to stop a power generation function of the generator. As the charged amount of the low-voltage battery decreases, the power generation function of the generator is automatically started to recharge the low-voltage battery.